The present invention relates to substrate processing systems. More specifically, the present invention relates to the avoidance of unnecessary tripping of ground fault interruption (GFI) circuitry used in such substrate processing systems.
Ground fault interrupt circuitry is an important subsystem in today's substrate processing systems. GFI circuitry detects differences in the current flowing into and out of certain subsystems of a substrate processing system, and disconnects power from the system if the difference between the two exceeds a given threshold. This occurs when current leaks from normal circuits in the system and flows via alternate circuits to ground. This is a more specialized case of the general ground fault, where any non-equipment circuit to ground is to be avoided. Ground faults should be avoided for a variety of reasons, among them noise in electronic circuits (e.g., processing system control circuitry) and operator safety (avoiding the situation where an operator offers the path of least resistance to ground).
As device sizes have become smaller and integration density has increased, issues that were not previously considered important by the industry have become of concern. As a result, several factors have often required the alteration of process parameters to account for the type of film being deposited and the uses to which that film will be put. Thus, for a given application, such parameters will be varied to provide a film having optimal characteristics for the chosen application. For example, the temperature at which a film is deposited can affect the quality of the film deposited. In certain applications, relatively higher temperatures are preferable because the reactions used to deposit the film cannot take place at lower temperatures. Ceramic pedestals are preferable to pedestals constructed of materials such as metal because ceramic pedestals are less susceptible to reaction with the reactants used in these processes and to failure (e.g., melting) at relatively high temperatures employed.
Unfortunately, certain of these processes have encountered unscheduled shutdowns by the substrate processing system's GFI circuitry. The detection and appropriate handling of ground faults is important for several reasons, including operator safety. If a ground fault exists in a piece of electrical equipment, an operator coming in contact with the equipment may offer a relatively low-resistance path to ground and so be subjected to the risk of electrical shock (although the risk varies with the amount of leakage current). In fact, various safety standards have been promulgated that govern the acceptable levels of leakage current in such systems (e.g., &lt;3.5 mA for operator safety (U.S. National Electrical Code Section 250-21) and &lt;30 mA for equipment protection (Semiconductor Equipment and Materials International (SEMI) Facilities Standards and Safety Guideline SEMI S9-95)).
However, interruptions due to ground faults should be minimized. The intermittent and unscheduled interruption of substrate processing is undesirable for a number of reasons. First, an unscheduled shutdown seriously degrades system throughput because the substrates currently being processed are most likely ruined by such an event, other substrates (in a multi-chamber system) may also be ruined, and one or more processing chambers will likely require reactants to be flushed out. The chamber(s) will also likely require one or more cleaning steps. Additionally, the offending machine's processing line is likewise interrupted, requiring re-initialization of the other machines in the line. All these extra steps and the time they require are even more problematic to an end-user of such systems because the interruptions are unscheduled and intermittent. Accordingly, a solution to the problem of spurious ground faults in such systems is needed.